Showerheads may pose a risk for those with compromised immune systems by harboring and aerosolization of bacterial biofilms

As noted in many prior posts, the world is full of microorganisms to which we humans are exposed constantly, and there is still a significant scientific debate regarding whether we need such exposures to prime the immune system and to keep it from getting out of control (e.g., overreacting and causing such diseases asthma).
However, a seemingly unexpected source has appeared, the plastic showerhead. Researchers took samples of the biofilm [see] that builds up inside showerheads from 45 sites in nine American cities and analyzed the genetic material which it contained. Interestingly, some samples had high concentrations of a microbe known as Mycobacterium avium (which is related to the one that causes tuberculosis) which can cause respiratory illnesses. This is found in tap water, but remains harmless unless turned into an aerosol and inhaled, precisely what happens when bacteria-ladened water is forced at high pressure through a showerhead. As the tiny particles are inhaled, they get into the lungs and may start an infection.
Is this a cause for alarm? Not for healthy people, the researchers note, but those with a compromised immune system or who are at risk of pulmonary diseases (e.g., the elderly) may want to take precautions. Cleaning showerheads with bleach will not solve the problem since the microbes will simply return with a fresh flow of water.
The researchers suggest replacing plastic showerheads with metal ones.   They also suggest letting the water flow for a bit to get rid of some of the build-up in the showerhead. However, even those precautions would leave one exposed to the aerosols formed by the fresh flow of water. Thus, the immune compromised may want to consider bathes as an alternative.
If I had one criticism of the study it was its apparent failure to sample the incoming water for its chlorine level. A number of years ago in the “blue water” cases (in which I represented one of the defendants) it was shown that biofilms developed because of the lack of residual chlorine in the neighborhood water supply (the housing tract was at the end of the distribution system). Since then EPA has upped the required chlorine level, but there are still a number of places in the U.S. where such biofilms have been found to develop. Frequently the problem is that the chlorine degrades as it travels through the system over time; also the presence of substantial biological material in the water “uses up” the chlorine. Rather than incurring the expense of remote chlorination stations, many water utilities have turned to using chloramines, which has a longer half-life. The problem is that in old water systems chloramines has been found to scavenge lead from old solder and piping, resulting in very much increased lead exposures to children; chloramines have been also found to pit piping, resulting in leaks and causing structural damage to buildings.
Thus, this study highlights a serious problem with the fundamentals of providing a healthy water supply to the population, a problem that is not being adequately addressed.